Having worked in Nuke a little over this last week or so i love the grade node for matching black levels. You can select the levels then leave it as the last node in your CC stack and the blacks will always match without having to re sample. Makes having to go go back and tweak other colours so much easier if you know your blacks will always be correct.
Do we have something of that ilk in flame? I always rely on the CC node and use the RGB channels to match.
Colour Warper can make a nice, White, Black and some others matching you need.
Watch:
Yeah, there’s nothing as nice and simple as “this is my black, this is my white” like Nuke has. I wish there was, because every option in flame involves a lot of work comparatively.
I don’t even know what the “best” option is at this point, if the MasterGrade node has improved on wha the Color Warper does. None of them is ideal, and I often, like you, end up using the histogram in the color correct. The irony there is you can match any two colors that aren’t black and white using the curves in the CC.
Really wish that simple “this is black, this is white” two sample option existed in the software.
SMALL UPDATE FROM MY SHIT TALKING:
The Color Corrector’s curves do a very nice job of matching black levels and do not retain the 0.0 vertex anymore. This is very exciting to me and I apoligize for the misinformation above! So to answer both the original post and my own complaints in this post:
Use the Color Correct’s curve tools. Plug in a front and back, sample them both and hit match. Black levels matched.
Isn’t this what the highlights/darks sample and match function in the color corrector are for?
But maybe they don’t work on floating point values?
Looks like I was wrong! I just did a little test to match blacks with the curves and it worked! Hooray! 
So will this work in a similar way that once its set i can CC before the node and the black levels will account for any change or will i have to re sample?
That works in Nuke?
Like you can match black levels, then lift the bg by 20% and the FG levels auto-re-match?
I’m about 99% sure flame will not do this, but I’ve already been wrong once in this thread.
Yeah you can set the black level then grade before that and you know your blacks will be ok.
Nuke’s grade node does this? it sounds like sorcery to me.
hmmm… I Nuke I have only seen this kind of behavior on more articulated gizmos where the minimum local value is automatically evaluated, so downstream grades can compensate for upstream changes. Useful for haze reduction.
As far as I know in Nuke’s Grade node you will have to manually resample the black point for the Black adjustment (Lift) to follow.
We need a demo @Ben 
Apologies i was mixed up its the Blacksmatch gizmo. Its a pretty amazing tool.